The present invention relates to a transit positioning device for use with a conventional manhole mount. A transit is commonly used to make survey measurements for proper alignment of a pipeline with a manhole. This transit must be properly aligned over the center of a manhole and for this purpose, a manhole mount is used to locate the transit over this center. Various manhole mounts have been used to hold the transit above a center of the manhole. A portion of a conventional manhole mount is shown in FIG. 1. This manhole mount xe2x80x9cAxe2x80x9d includes a tubular vertical arm xe2x80x9cBxe2x80x9d and a tubular horizontal arm xe2x80x9cCxe2x80x9d joined together at a joint xe2x80x9cDxe2x80x9d. The knob xe2x80x9cExe2x80x9d allows the horizontal arm xe2x80x9cCxe2x80x9d to be adjustably positioned with respect to vertical arm xe2x80x9cBxe2x80x9d. Vertical arm xe2x80x9cBxe2x80x9d, at its lower end, has structure for mounting the manhole mount xe2x80x9cAxe2x80x9d to a manhole.
When the manhole mount is used for supporting a transit, a plumb bob may be used for positioning the transit directly over a target located at the bottom center of the manhole to which the pipeline is to be connected.
With conventional manhole mounts, it has been difficult to precisely position the plumb bob over the target. Crude adjustments are normally made, and it has been very time consuming to properly position the transit over the target.
The present invention overcomes these problems by providing a transit holding platform which is mounted to a manhole mount and is stabilized in a horizontal plane. A mechanism is provided with the platform to allow for precise positioning of the transit in orthogonal directions in the horizontal plane. With the transit precisely located directly above the target, surveying measurements can be taken to align a pipeline with the manhole.
A transit positioning device for use with a conventional manhole mount having an elongate vertical arm and an elongate horizontal arm orthogonally joined together at a joint. The positioning device includes a transit holding platform for mounting a transit at a pre-selected location on the platform. The platform is mounted to an end of an adjustable length elongate member which in turn is mounted to the horizontal arm of the manhole mount. A coupler is provided at the end of the elongate member adjacent the platform for rotatably securing the platform to the elongate member with an axis of rotation extending generally in a vertical direction and in spaced apart relation from the location where the transit is mounted. An indicator device, such as a plumb bob, is provided for indicating a position of the platform in the horizontal plane with respect to a target located at a bottom of the manhole. An adjustable length stabilizing arm is provided with one end hingedly connected to the vertical arm below the joint at a position spaced apart from the joint, and a second end hingedly connected to the horizontal arm at a position spaced apart from the joint. The stabilizing arm is used to position the horizontal arm of the manhole mount to extend in a horizontal plane.
With this arrangement, the stabilizing arm can be adjusted in length to position the transit holding platform in a horizontal plane. The length of the elongate member can be adjusted to position the transit holding platform over the target in a direction coaxial with the longitudinal axis of the horizontal arm. The platform can also be rotated about an arc centered on the coupler. With this arrangement, the platform can be easily positioned in the horizontal plane directly over a target located at a bottom of the manhole.